华北地区典型工业城市周边黑碳气溶胶干沉降通量的观测研究

A large amount of fossil fuel is consumed by industrial and residential activities in the Beijing-Tianjin-Hebei region, during which highly concentrated soot particles are released due to incomplete combustion. Soot particles, characterized by small size, large specific surface area and strong absorption of light, play an important role in regional haze formation and global climate change. At present, spatial distribution, emission characterization, optical properties and mixing state of soot particles are well characterized in extensive studies. However, the removal process of soot particles is less investigated and the mechanism remains uncertain. The dry deposition rate of sub-micron particles is mainly obtained from theoretical simulation and calculation, while experimental measurements and observations are scarce. Under the influence of turbulence in the atmospheric boundary layer, soot particle dry deposition rate varies by 2~3 orders of magnitude depending on aging process and meteorological conditions. Since soot particles has a direct effect on the rapid increase of regional fine particulate concentration, the uncertainty is major source of errors in the atmospheric chemistry model. In this study, we focus on the dry deposition process of soot particles. Comprehensive field measurements will be conducted in typical industrial cities in North China to obtain the dependence of dry deposition rate on boundary layer condition, particle size and aging process. Findings in this study will improve the accuracy of dry deposition module in the atmospheric chemical transport model and be beneficial to the determination of haze formation mechanism in North China.

我国华北地区人为活动消耗了大量化石燃料，其不完全燃烧过程排放了大量黑碳气溶胶颗粒。黑碳气溶胶粒径小、比表面积大、吸光能力强，是影响区域大气灰霾形成以及全球气候变化关键因素之一。国内外科学家在黑碳气溶胶空间分布、光学特性，及其混合状态研究方面取得了大量成果，然而对于黑碳气溶胶在大气中清除过程的研究还非常薄弱，亚微米级颗粒物干沉降速率主要依赖于理论推导，实际验证资料极少。黑碳气溶胶的干沉降受大气边界层湍流过程的影响，不同气象条件下黑碳气溶胶的干沉降速率有近2～3个数量级的差异，影响区域大气细颗粒物的形成，也是大气化学数值模型模拟误差和不确定的重要来源之一。本研究将黑碳气溶胶的干沉降过程作为研究对象，选择在华北地区典型工业城市周边开展综合外场观测实验，获取不同边界层湍流条件下、不同粒径和老化程度黑碳气溶胶的干沉降速率，改善大气化学输送模型的干沉降模块，对华北地区重污染过程的成因解析提供支撑。

本课题在华北地区典型城市开展多个外场观测实验，对黑碳气溶胶的理化特性、形貌演变和沉降过程进行了研究，取得的科研成果主要包括：（1）基于涡动相关法在河北农村地区观测了冬季农田下垫面黑碳气溶胶的干沉降通量和速率，分析了不同大气层结条件下黑碳气溶胶的干沉降速率，探讨了黑碳包裹物厚度对黑碳干沉降的影响，明晰了黑碳气溶胶的干沉降特征。同时，研究了清洁天、污染天、雾天和雪天黑碳气溶胶的形貌演变特征及其影响因素，利用后向轨迹模式识别了典型过程中黑碳气溶胶的来源。（2）利用分段采集的降水样品，分析了雨水中黑碳气溶胶的浓度、粒径分布及其随降水过程的变化，区分了云内清除和云下清除对黑碳气溶胶湿清除的贡献。（3）在城市地区开展了黑碳气溶胶形貌特征观测研究，分析了黑碳气溶胶的浓度和粒径谱分布，表征了黑碳气溶胶包裹物厚度的演变规律及其影响因素。（4）黑碳气溶胶沉降特征和形貌演变规律的观测结果，有利于优化大气化学传输模式中黑碳气溶胶浓度和辐射效应的模拟效果。